We observed a distinct ThS‐positive signal in the CA1 region of the hippocampus in mice injected with tau‐AC‐wt fibrils, while the ThS‐signal was significantly lower in mice injected with tau‐AC‐S356D (Figure S6E, Supporting Information).[28] Using the TUNEL assay, we observed that the high intensity tau‐AC‐positive signal was preferentially overlapped with apoptotic neurons (Figure 5D), providing a possible link between the observed neuronal loss and memory impairment in tau‐AC‐injected mice. The gene discussed is MAPT; the disease is memory impairment.